Infusion packets and a process for their manufacture

ABSTRACT

The present invention relates to a process for the manufacture of infusion packets, the process comprising: • (a) providing a first sheet of thermoplastic material (2) which is porous or non- porous; • (b) thermoforming portions of the first sheet into a three-dimensional shape; • (c) providing a second sheet of material; • (d) dosing an infusible substance into the thermoformed portions of the first sheet or onto the second sheet; • (e) sealing the first and second sheets together to form pockets containing the infusible substance such that each pocket includes at least one thermoformed portion of the first sheet; • (f) severing the pockets at the seals to form infusion packets each having a chamber containing the infusible substance,

TECHNICAL FIELD

The present invention relates to infusion packets. More particularly,the present invention is directed towards the manufacture of infusionpackets (such as tea bags) having a three-dimensional shape.

BACKGROUND

In the past, conventional infusion packets (e.g. tea bags) havetypically been flat, comprising a single chamber filled with infusiblematerial (e.g. leaf tea, herbal mixtures). Such packets are essentiallyflat and thus restrict the movement of the infusible material within thepacket to substantially two dimensions. As a result, the infusionperformance of these infusion packets is limited.

U.S. Pat. No. 3,549,381 discloses a tea bag comprising tea leavesenclosed in an impervious, flexible, thermoplastic protective film, atleast a portion of said film having a regularly spaced embossed patternon at least one surface which has been drawn sufficiently to develop apreferential weakness in one direction. The tea bag is impervious untilit is stretched by the end user. As the thermoplastic material isstretched, it opens up forming a netlike material. Thus the embossedthermoplastic material is stretched in a first direction duringmanufacture (to develop a preferential weakness in one direction) andthen stretched to some extent in a second direction by the end user (toform a netlike material). Since these tea bags are substantially flat,the movement of the tea leaves enclosed therein is restricted tosubstantially two dimensions during infusion. Furthermore, sinceformation of the netlike material relies on the consumer stretching thethermoplastic material, such tea bags will not be as uniform asconventional tea bags. For example, too little stretch may limit theperformance of the tea bag due to only a part of the packaging materialbecoming porous. On the other hand, too much stretch may introduceopenings which are large enough to permit leakage of the tea leaves intothe beverage itself. Thus the performance of the tea bags disclosed inthis document is likely to be far from optimal.

The past few decades have seen the development of infusion packets whichhave a more three-dimensional shape and which allow greater circulationand mixing of the infusion liquid and the infusible material. Ofparticular success have been tetrahedral-shaped packets such as thosedescribed in WO 04/033303 and WO 95/01907. In the manufacture oftetrahedral packets, the tetrahedral shape is conventionally formed bymaking mutually perpendicular transverse seals in a tube of filtermaterial. Apparatus designed for such manufacture is ill-suited to themanufacture of other three-dimensional shapes.

Other three-dimensional shapes have been considered, such as thosedescribed in GB 2 408 252, which are manufactured by forming porous websinto three-dimensional shapes via the application of heat and/ormoisture. The packages are made from webs of conventional infusionpacket material, and the resulting packages are said to inherently havesome folding, pleating and gathering of the web material, e.g. at thebase of the shape being formed. Therefore, some areas in the package arenot porous and/or have a tendency to trap the infusible material. Thiscan limit the infusion performance of such packages, as well as beingvisually unappealing to consumers.

Therefore, there remains scope for improvements regarding the design andmanufacture of three-dimensional infusion packets.

SUMMARY OF THE INVENTION

Known thermoforming processes (e.g. for producing capsules) are capableof forming thermoplastic material into a variety of three-dimensionalshapes. However, materials conventionally used to manufacture infusionpackets are often not suitable for thermoforming. Firstly, infusionpackets are commonly made of paper, which is not thermoformable.Secondly, even if they are made from a thermoformable material, theporosity and thinness of the material makes thermoforming a challenge.

In order to thermoform a material, it is necessary to heat the materialto a temperature which is sufficient to allow the thermoplastic materialto deform under thermoforming stresses. Very thin material is liable totear under the stresses applied, particularly when being formed into athree-dimensional shape comprising sharp features. There is also thepossibility that the thermoforming process will increase the size of theperforations and/or holes in the material to such an extent that fineparticles of infusible material will leak out of the packet. On theother hand, it is important that heating the material does not close theperforations in the material, since this would reduce the porosity ofthe infusion packet.

Thus it would seem that thermoforming is not a practical method ofgenerating infusion packets. However, the inventors have overcome thesebarriers by using a non-conventional material as the substrate forthermoforming.

Thus in a first aspect, the present invention relates to a process forthe manufacture of infusion packets, the process comprising:

-   -   (a) providing a first sheet of thermoplastic material which is        porous or non-porous;    -   (b) thermoforming portions of the first sheet into a        three-dimensional shape;    -   (c) providing a second sheet of material;    -   (d) dosing an infusible substance into the thermoformed portions        of the first sheet or onto the second sheet;    -   (e) sealing the first and second sheets together to form pockets        containing the infusible substance such that each pocket        includes at least one thermoformed portion of the first sheet;    -   (f) severing the pockets at the seals to form infusion packets        each having a chamber containing the infusible substance,        wherein the first sheet is a polymer film with at least one        embossed surface, and wherein the thermoformed portions of the        first sheet are porous.

The process involves thermoforming a thermoplastic polymer film with atleast one embossed surface. This type of thermoplastic material is notconventionally used in the manufacture of infusion packets. Indeed, thefirst sheet does not need be porous prior to being thermoformed(although the thermoformed portions of the first sheet are porous, i.e.permeable to aqueous liquids). By using this non-conventional material,it has been possible to develop a process which uses thermoforming tomanufacture infusion packets having a wide variety of three-dimensionalshapes.

The inventors believe that this is the first time that anyone hasrecognised the possibility of using thermoforming to manufactureinfusion packets with three-dimensional shapes from this material.

Thus in a second aspect, the invention relates to an infusion packetcomprising a chamber that contains an infusible substance, wherein thepacket comprises material that has been formed into a three-dimensionalshape by thermoforming a thermoplastic polymer film having at least oneembossed surface such that the thermoformed thermoplastic polymer filmis porous.

DETAILED DESCRIPTION

In a first aspect, the present invention relates to a process for themanufacture of infusion packets.

This process involves a first step in which a first sheet ofthermoplastic material is provided. The first sheet of thermoplasticmaterial may or may not be porous. In a second step, portions of thissheet are thermoformed into a predetermined three-dimensional shape(i.e. a shape having length, breadth and depth). The thermoformedportions of the first sheet are porous (i.e. permeable to aqueousliquids).

A variety of three-dimensional shapes are possible. For example,tetrahedral or hemispherical shapes and the like are possible.Hemispherical shapes are particularly preferred.

The first sheet of thermoplastic material is a polymer film with atleast one embossed surface. In certain embodiments the embossed film maybe embossed on both surfaces. This first sheet need not be porous priorto being thermoformed. During thermoforming, portions of the first sheet(i.e. the portions being formed into three-dimensional shapes)experience stresses. These stresses are sufficient to introduce holes inthe embossed polymer film. This allows the manufacture of a porousinfusion packet from a non-porous material. Furthermore, since the holesare formed during the thermoforming process, this sheet can be stretchedfurther than an equivalent porous sheet whilst ensuring that the holespresent in the final packet are sufficiently small to minimise sift ofthe infusible material. Since the application of the thermoformedmaterial is as infusion packets, the thermoformed thermoplastic materialis permeable to aqueous liquids. More precisely, the thermoformedportions of the thermoplastic material are porous.

The polymer film preferably comprises polypropylene, polyethylene, orcopolymers thereof. High-density polyethylene is particularly preferred.

The embossed surface preferably comprises small raised solid bosses(i.e. raised figures) arranged with spaces between adjacent bosses inlongitudinal and transverse rows. Preferably the bosses in eachlongitudinal row are in staggered arrangement with the bosses in eachadjacent row. The shape of the bosses is not critical, although in aparticularly preferred embodiment the bosses are hexagonal in shape.

Preferably the embossed surface of the polymer film has a regularpattern of bosses. It is particularly preferred that the bosses areregularly spaced in longitudinal and transverse rows. In certainembodiments, the bosses are regularly spaced in mutually perpendicularrows.

Prior to thermoforming, the embossed surface of the polymer filmpreferably has at least 60 bosses per 25 mm, more preferably at least 80bosses per 25 mm, most preferably at least 100 bosses per 25 mm.

The embossed polymer film can be produced by extruding polymer film,usually as a molten film, into the nip between two suitable rollers.Embossing is achieved by passing the polymer film between pair ofrollers wherein at least one of the pair is engraved. The engravingpattern determines the shape and spacing of the bosses on the embossedsurface of the film. In order to produce a polymer film which isembossed on both surfaces, the polymer film is passed between a pair ofrollers wherein both of the rollers are engraved.

As set out above, it is not necessary for the embossed polymer film tobe porous prior to thermoforming. However, in certain embodiments theembossed polymer film is porous prior to thermoforming. This can beachieved by simultaneous or sequential stressing of the embossed film intwo directions in the plane of the film. For example, this type ofporous material can be produced as described in GB 914,489, GB 1,055,963and GB 1,106,254.

In a third step of the process, a second sheet of material is provided.This second sheet of material need not be the same material as the firstsheet. In fact the second sheet of material need not be thermoformable,and as such can be a material conventionally used for the manufacture ofinfusion packets. In order to facilitate manufacture of the finalinfusion packet it is preferred that the second sheet of material isheat-sealable. In particular, it is preferred that the second sheet ofmaterial is a sheet of thermoplastic material. Suitable examples includepolyethylene terephthalate (PET) and poly lactic acid (PLA).

In one preferred embodiment the second sheet of material is also apolymer film with at least one embossed surface. This permitsthermoforming of portions of the second sheet. In this embodiment, thesecond sheet of material may be porous or non-porous prior to beingthermoformed. The thermoformed portions of the second sheet arepreferably porous.

In a fourth step, the process involves dosing an infusible substance.The infusible substance can be dosed into the thermoformed portion ofthe first sheet or onto the second sheet. For convenience ofmanufacture, it is preferred that the infusible material is dosed intothe thermoformed portion of the first sheet.

Preferred examples of infusible substances are tea plant material, herbplant material, fruit pieces and/or flower material (e.g. petals). Theterm “tea plant material” refers to leaf and/or stem material fromCamellia sinensis var. sinensis or Camellia sinensis var. assamica. Italso includes rooibos obtained from Aspalathus linearis, as well as theproduct obtained by blending any of these tea plant materials. The leafmaterial may be fermented (i.e. black tea), partially fermented (i.e.oolong tea), or substantially unfermented (i.e. green tea).

In a fifth step, the first and second sheets are sealed together to formpockets. The pockets contain the infusible substance. Each pocketincludes at least one thermoformed portion of the first sheet. The firstand second sheets can be conveniently sealed together around theperimeter of the thermoformed portion of the first sheet.

As mentioned above, the second sheet need not be thermoformed.Therefore, in one preferred embodiment the pockets comprise athermoformed portion of the first sheet sealed together with anon-thermoformed portion of the second sheet (i.e. the portion of thesecond sheet is essentially flat).

In embodiments where portions of the second sheet have also beenthermoformed, it is preferred that each pocket includes a thermoformedportion of the first sheet and a thermoformed portion of the secondsheet. Once again, the first and second sheets can be convenientlysealed together around the perimeter of the thermoformed portions.

Sealing may be achieved by any suitable method known in the art. Sincethe process necessarily involves thermoplastic material heat-sealing isparticularly preferred. Alternatively, sealing the first and secondsheets together may be achieved by other methods. For example,ultrasonic sealing allows the seal to be very narrow, which can improvethe appearance of the infusion packet.

A sixth step of the process involves severing the pockets at the sealsto form infusion packets. Each infusion packet has a chamber containingthe infusible substance. It should be noted that this step is notnecessarily performed subsequently to the fifth step of sealing, and ina preferred embodiment, the sealing and severing steps of the processcan be performed simultaneously.

As the thermoformed portions of the sheet form part of an infusionpacket, typically the sheet of thermoplastic material will be very thin.Prior to being thermoformed, it is preferred that the sheet ofthermoplastic material has an average thickness of less than 1.0 mm,more preferably less than 0.5 mm, still more preferably less than 0.2mm, most preferably from 0.01 to 0.1 mm.

The thermoforming may be carried out by any suitable means known in theart. However, since the infusion packet produced by the process isporous, it is impractical to use air pressure to thermoform the sheet ofthermoplastic material. Therefore, it is preferred that the sheet isthermoformed using a mould, more preferably by pressing a male formerinto the sheet.

As the sheet of thermoplastic material is relatively thin, with a lowcapacity to store heat, it is preferred to heat the mould rather thanthe material.

In a preferred embodiment, thermoforming comprises the steps of bringingportions of the sheet of thermoplastic material at a temperature belowthat required for thermoforming into contact with a mould at atemperature above that of a thermoforming temperature of thethermoplastic material, pressing the mould into contact with thethermoplastic material, the contact between mould and thermoplasticmaterial causing heat to transfer from the mould to the thermoplasticmaterial and raising the thermoplastic material to a thermoformabletemperature; such pressing causing thermoforming of the thermoplasticmaterial to conform to the shape of the mould.

Thus no heating of the thermoplastic material is carried out untilthermoforming begins. As the thermoplastic material has a low capacityto store heat, it will rapidly heat up once it comes into contact withthe heated mould. Thus this method takes the potential disadvantage oflow heat capacity and utilises this feature, resulting in effectivethermoforming of the thermoplastic material.

The temperature of thermoforming is sufficient to allow thethermoplastic material to deform under thermoforming stresses.Therefore, the temperature of the mould is preferably at least 60° C.,more preferably at least 70° C. In order to ensure that the infusionpackets produced by this process are porous, the thermoplastic materialshould not be exposed to temperatures which cause the perforations toclose. Thus the temperature of the mould is preferably less than 150°C., more preferably less than 125° C., most preferably less than 100° C.

In a second aspect, the invention relates to an infusion packetcomprising a chamber that contains an infusible substance, wherein thepacket comprises material that has been formed into a three-dimensionalshape by thermoforming a thermoplastic polymer film having at least oneembossed surface such that the thermoformed thermoplastic polymer filmis porous.

It will be appreciated that such an infusion packet can be manufacturedby the process of the invention.

The invention will now be illustrated by way of example and withreference to the following figures, in which:

FIG. 1 is a schematic representation of an embodiment of an apparatusthat is suitable for carrying out a process according to the presentinvention; and

FIG. 2 is a schematic representation of the apparatus shown in FIG. 1during execution of a process according to the present invention.

FIG. 1 shows a first sheet of thermoplastic material 2. Thethermoplastic material is a film of high-density polyethylene which isembossed on one surface. The embossed film has 60 features per 25 mm.

The film is clamped in place by upper clamps 4 and lower clamps 6. Thefilm is at ambient temperature.

Positioned above the embossed film is a male former 8, at a temperatureof 70° C.

In use, the male former 8 moves downwards to come into contact with thefirst sheet 2. As it makes contact, the portion of the first sheet 2that comes into contact with the male former 8 rapidly heats up to 70°C.

The male former 8 continues to move downwards, heating and thermoformingthe first sheet 2 simultaneously, until the male former 8 is in theposition shown in FIG. 2.

During thermoforming, portions of the embossed polymer file (i.e. thosein contact with the male former) experience stresses. These stresses aresufficient to introduce holes in the embossed polymer film.

Once the first sheet 2 is fully thermoformed, the male former 8 retractsand the first sheet 2 rapidly cools and sets. The formed portions of thefirst sheet are now porous, and hence permeable to aqueous liquids, dueto the holes introduced during thermoforming.

An infusible substance can subsequently be dosed into the thermoformedportion of the first sheet, and a second sheet of material used to sealthe infusible material within a chamber. This second sheet can be asubstantially planar sheet of material, or alternatively the secondsheet can also have been thermoformed.

As used herein the term “comprising” encompasses the terms “consistingessentially of” and “consisting of”. It should be noted that inspecifying any range of values or amounts, any particular upper value oramount can be associated with any particular lower value or amount. Thedisclosure of the invention as found herein is to be considered to coverall embodiments as found in the following claims as being multiplydependent upon each other, irrespective of the fact that claims may befound without multiple dependency. Unless defined otherwise, alltechnical and scientific terms used herein have the same meaning ascommonly understood by one of ordinary skill in the art in the relevantfield.

1. A process for the manufacture of infusion packets, the processcomprising: (a) providing a first sheet of thermoplastic material whichis porous or non-porous; (b) thermoforming portions of the first sheetinto a three-dimensional shape; (c) providing a second sheet ofmaterial; (d) dosing an infusible substance into the thermoformedportions of the first sheet or onto the second sheet; (e) sealing thefirst and second sheets together to form pockets containing theinfusible substance such that each pocket includes at least onethermoformed portion of the first sheet; (f) severing the pockets at theseals to form infusion packets each having a chamber containing theinfusible substance, wherein the first sheet is a polymer film with atleast one embossed surface, and wherein the thermoformed portions of thefirst sheet are porous.
 2. A process as claimed in claim 1 wherein thesecond sheet is a sheet of thermoplastic material.
 3. A process asclaimed in claim 2 wherein portions of the second sheet are thermoformedinto a three-dimensional shape.
 4. A process as claimed in claim 3wherein the second sheet is a polymer film with at least one embossedsurface.
 5. A process as claimed in claim 3 wherein each pocket includesa thermoformed portion of the first sheet and a thermoformed portion ofthe second sheet.
 6. A process as claimed in claim 1 wherein at leastone of the embossed polymer films is made porous prior to thermoformingby simultaneous or sequential stressing of the embossed film in twodirections in the plane of the film.
 7. A process as claimed in claim 1wherein the first and/or the second polymer m comprises polyethylene,preferably high-density polyethylene.
 8. A process as claimed in claim 1wherein the at least one embossed surface of the first and/or the secondpolymer film has a regular pattern of bosses.
 9. A process as claimed inclaim 1 wherein prior to thermoforming the at least one embossed surfaceof the first and/or the second polymer film has at least 60 features per25 mm, preferably at least 80 features per 25 mm.
 10. A process asclaimed in claim 1 wherein the three-dimensional shape is ahemispherical shape.
 11. A process as claimed in claim 1 wherein eachsheet of thermoplastic material has an average thickness of less than1.0 mm, preferably of less than 0.5 mm.
 12. A process as claimed inclaim 1 wherein thermoforming comprises the steps of bringing portionsof the sheet of thermoplastic material at a temperature below thatrequired for thermoforming into contact with a mould at a temperatureabove that of the thermoforming temperature of the thermoplasticmaterial, pressing the mould into contact with the thermoplasticmaterial, the contact between mould and thermoplastic material causingheat to transfer from the mould to the thermoplastic material andraising the thermoplastic material to a thermoformable temperature; suchpressing causing thermoforming of the thermoplastic material to conformto the shape of the mould.
 13. A process as claimed in claim 12 whereinthe temperature of the mould is at least 60° C., more preferably atleast 70° C.
 14. An infusion packet comprising a chamber that containsan infusible substance, wherein the packet comprises material that hasbeen formed into a three-dimensional shape by thermoforming athermoplastic polymer film having at least one embossed surface suchthat the thermoformed thermoplastic polymer film is porous, and a secondsheet sealed with the first sheet to form the chamber.
 15. An infusionpacket as claimed in claim 14 wherein the thermoplastic polymer filmcomprises polyethylene, preferably high-density polyethylene.